Long-term (7-9 years) and short-term (1 year) grazing exclosures were used to determine the effects of grazing on plant and insect abundance, species richness and evenness over different time intervals. Short-term grazing exclusion decreased plant species richness and created a less balanced plant community, possibly because dominant species were able to out-compete less dominant species for resources after being released from grazing pressure. Long-term grazing exclusion also decreased species richness, however, the plant community composition was more even, indicating that species dominance was reduced over time. Grazing exclusion enhanced insect abundance, most likely due to the increased levels of available forage, but did not affect diversity or evenness of insect communities. The results suggest that vertebrate grazing may increase plant richness, even in nutrient-poor, semi-arid grasslands, but may decrease insect abundances.
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